Hydraulic power system



Nov. 10, 1964 A. M. LA ROU HYDRAULIC POWER SYSTEM Filed Nov. 20, 1959 Q Q L A La R3 Si N Wig u kg Q & Q

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United States Patent 3,156,098 HYDRAULIC POWER SYSTEM Albert M. La Ron, Huntington Woods, Mich., assignor,

by mesne assignments, to Ford Motor Company, a corporation of Delaware Filed Nov. 20, 1959, Ser. No. 854,479 3 Claims. (Cl. 60-97) This invention relates to hydraulic power transmission systems, particularly systems for use on earth moving equipment and the like.

My improved hydraulic system is especially advantageous for use on backhoes or diggers of the type having a movable bucket or dipper mounted on a swingable dipper stick, the dipper stick being carried on a boom which is also swingable, with the entire assembly mounted for horizontal swinging on a swing post. These diggers are commonly mounted on a tractor or truck, and stabilizers are usually provided for stabilizing the digger frame with respect to the ground when digging is carried on. In these devices, the dipper, dipper stick, boom, swing frame and stabilizers are almost always actuated by hydraulic cylinders supplied from a pump of suitable capacity driven by the tractor engine. For a typical example of such equipment, reference is made to Brinkel Patent No. 2,903,145, granted September 8, 1959.

In the operation of these diggers, two or more of the cylinders may be in operation simultaneously so the pump must be of ample capacity, with regard both to pressure and volume, to supply the requirements. A relief valve is incorporated in the fluid pressure system which may be set to open at desired pressure such that the system is protected from excessive buildup of pump pressure during stalling of anyof the actuating cylinders.

The relief valve is in operation frequently during the digging operation, particularly when the digger is operated by inexperienced or unskilled help. Stalling on the lift, crowd or pitch cylinders due to contact of the dipper with a stump, rock or other relatively immovable object will cause operation of the relief valve. Besides wasting power, this causes excessive heating of the fluid which has necessitated the'utilization of oil coolers of large capacity and even these have proven inadequate in some instances.

In my improved construction, two hydraulic pumps are connected in parallel and an unloading valve is incorporated in the output line of oneof the pumps such that the latter may be unloaded at some pressure below that at which the relief valve opens and the flow permitted to return to the reservoir through a low resistance path, while the pressure of the other pump is still maintained to supply the high pressure required. This eliminates the large energy waste and heating of a large volume of fluid should the system pressure rise to the relief valve setting.

Another feature of this improved construction is that for digger operation, the unloading valve may be conveniently placed between two of the control valve spools so that for simultaneous operation of spools on each side of the unloader valve, the pump flows may be directed separately to the cylinders concerned. Thus the operation of each of these cylinders is independent of the load on the other cylinder.

Other advantages of the invention will become apparent from the following specification which, taken in conjunction with the accompanying drawing, describes a preferred embodiment of the invention.

The drawing is partly in section and partly schematic. Specifically it shows a digger control valve in approximate horizontal vertical section with schematic representations of the associated components of the hydraulic system.

- capacity.

' the system against abnormal pressures.

3,156,098 Patented Nov. 10, 1964 "Ice Referring to the drawing, it will be seen that the control valve housing ltl encases a plurality of valve spools which form elements of an open center system. The spools are movable axially either side of neutral by suitable control levers as is well known in the art.

A line 12 from reservoir 14 is connected to the suction sides of equal pressure pumps 16, 18. The pumps are preferably mounted in tandem for simultaneous rotation, the pump 16 in this instance being the pump of larger volumetric capacity and the pump 18 being of smaller Depending upon the particular application, the pumps may be of the same volumetric capacity and/ or pumps of unequal pressures may be used.

Line 20 connects the pressure side of pump 16 to the main inlet 22 of housing 10. A relief valve 24 set at some desired pressure, say 2500 p.s.i., protects this part of The relief valve vents into a drain passage 26 which, together with a similar drain passage 28, exhausts through port 30 and conduit line 32 to reservoir 14.

The valve housing is provided with a series of centraliy disposed pressure passages 34 which are closed and opened to fluid flow by movement of the Various valve spools, and lower and upper pressure passages or galleries 36, 38, which communicate with a plurality of check valves, 40, 42, etc. The bottoms of these check valve chambers are vented for proper pressure balance, and the plungers thereof are spring pressed into closed position. Each valve spool has a pair of check valves operatively associated therewith on the pressure side thereof in a manner explained below. A line 43 leads from the left hand end of the open center passage to the reservoir 14 or to another valve for operating some other accessory on the tractor.

Valve spools 44 and 46 control stabilizer cylinders 48 and 50 respectively. For example, movement of spool 44 upward will close off the open center flow from the right hand pressure chamber 23 through passage 34 and pressure fluid will flow through check valve 40, port 52 and line 54 into the upper chamber of cylinder 48,

the lower chamber thereof being vented into drain passage 28 through line 56 and port 58. Piston rod 6%) will thus be moved to thrust the stabilizer into contact with the ground. Withdrawal of the stabilizer is accomplished by downward movement of spool 44 from neutral position as shown on the drawing.

Similar movement of piston rod 62 of cylinder 50 which actuates the other stabilizer is controlled by appropriate movement of spool 46, the fluid flowing to and from the corresponding valve ports through lines 64 and 66.

Spool 68 controls actuation of crowd cylinder 70 through fluid lines 72, 74; spool 76 controls actuation of lift cylinder 78 through lines 80, S2; spool 84 controls actuation of pitch cylinder 86 through lines 88, 90; and spool 92 controls actuation of swing cylinder 94 through lines 95, $8. a

Lift cylinder 78 actuates the digger boom, crowd cylinder 7t) actuates the dipper stick, pitch cylinder 86 actuates the dipper itself which is pivotally mounted on the dipper stick and swing cylinder 94 swings the entire digger assembly about the swing post on the tractor (not shown) M4 to the central portion of the open center valve, and

the left hand section of the valve pressure chamber system is separated from the right hand section by an un loading valve 1% and a check valve 1%. The unloading valve 106 is set to open at a pressure of less than relief valve setting. The check valve 108 has a very light spring and will open under idling pressure of the pump 16. Its function is to prevent dumping of the pump 18 when the unloading valve 106 opens as presently will be explained. A relief valve 110 set to open at about 2500 p.s.i. protects this part of the system.

It may be seen then that the right hand portion of the valve, containing the right hand stabilizer and swing spools 44 and 92, will, under certain conditions of operation, be cut off from the left hand portion of the valve by opening of the unloading valve 106.

For example, during digging, if the load on either the crowd, lift or pitch cylinder 70, 78, 86, is such that the hydraulic system pressure approaches 2500 p.s.i., which ordinarily would cause opening of relief valve 110 or 24 or both, the unloading valve 106 will open (the spring thereof having been set at a lower pressure than the relief valve springs) and the output of pump 16 entering the housing at 22 will be dumped into drain passage 26. Instantly check valve 108 will close and the output of pump 18 will continue to be effective to supply the pressure required to continue digging. If the system pressure in the left side of the valve continues to rise, relief valve 110 will open. However, only the volume of the smaller pump 18 will flow through the relief valve and the energy waste and heating of the fluid will be substantially reduced.

It will be noted that the flow from pump 16 is always available to operate the swing cylinder 94 regardless of the position of the unloading valve. The same is true for the right hand stabilizer cylinder 48, but this is incidental and unimportant because the stabilizers are not concerned in the digging operation per se.

During operation of the lift, crowd or pitch cylinders, as when raising a load out of the excavation, the spool 92 is frequently actuated to swing the load simultaneously. In such case, the open center flow from the right hand side of the valve will be cut 011 and only the flow from the pump 18 is available to actuate the cylinders 70, 78, 86.

In instances where one or any combination of cylinders 70, 78, 86, is actuated, but not the swing cylinder 94, the output of both pumps is available.

Actually then there are three hydraulic circuits available during digging depending upon the positions of spool 92 and unloading valve 106. If spool 92 is in neutral and the unloading valve 106 is seated, the volume of both pumps is available for lifting, crowding and dipper actuation. If the unloading valve unseats, only the flow from pump 18 is effective. If the swing spool 92 is moved from neutral to full swing position, the entire flow from pump 16 is directed into the swing cylinder irrespective of the position of unloading valve 106.

In any instance where the unloading valve is unseated, if the load is relieved the unloading valve will close and the flow from pump 16 becomes instantly available in the left hand portion of the system.

One important feature of this system is that the path described by the dipper is fixed and independent of the load in the dipper under conditions when the operator calls for simultaneous full lift and full swing. Thus by proper selection of pump and cylinder sizes, the trajectory of the dipper may be predetermined. This feature reduces operator skill requirements and speeds up the digging operation. The return path of the dipper from dumping position to a point above the hole is also fixed. When the dipper is above the hole, release of the swing control lever by the operator instantly makes the output of both pumps available to fill the lift cylinder as the digging elements drop rapidly into the hole.

A check valve 112 along with a flow control valve 114 is placed in the line to the upper end of the lift cylinder 78. The valve 114 restricts return flow from the cylinder when the dipper is falling rapidly into the hole and tends to prevent cavitation. Relief valves 118 and 116 are incorporated in the lines to the lower ends of the lift and crowd cylinders. These valves are set at 3000 p.s.i.

While a specific example of the invention has been shown and described, it will be understood that such has been done for purposes of illustration and that it is not intended to limit the scope of the invention except as set forth in the appended claims.

I claim:

1. In a hydraulic power transmission having a pair of driven pumps for actuating a plurality of hydraulic cylinders, a selector valve comprising a housing and a plurality of valve spools in said housing selectively operable to direct fluid flow to said cylinders, ports operatively associated with said spools and passages connected with said ports forming an open center pressure distribution system, means connecting one of said pumps to one end of said open center system, means connecting the other pump to said system between certain of said spools, an unloading valve disposed in said housing between certain of the valve spools and operable to vent a portion of the system at pre-selected pressure, and a check valve disposed between the unloading valve and the remainder of the system and operable to close to prevent venting of said remainder of the system by operation of the unloading valve.

2. A hydraulic valve comprising, a housing, inlet ports and outlet ports in said housing, passages interconnecting said ports to form an open center system, movable spools associated with said passages operable when actuated to close off open center fluid flow and cause pressure buildup at an associated outlet port, a biased unloading valve disposed in said housing between certain of said spools and operable to vent a portion of the open center system, and a check valve disposed operatively adjacent said unloading valve and operable to isolate the remainder of the open center system in response to operation of said unloading valve.

3. In a hydraulic power transmission system, a first hydraulic pump, a first group of open center spool-type valves having a pressure side connected with the first pump, a series of hydraulic cylinders, each cylinder being connected with one of said valves controlled thereby, a second hydraulic pump, a second group of open center spool-type valves having a pressure side connected with the second pump, a second series of hydraulic cylinders, each cylinder being connected with said second valves for control thereby, an unloading valve connected with a pressure side of one of said groups of valves and a oneway fluid flow connection between the pressure sides of said two groups of valves, and an unloading valve connected with the pressure side of one of said groups of valves, the one way fluid flow connection preventing flow of fluid to the group of valves connected with the unloading valve from the pressure side of the other group of valves.

References Cited in the file of this patent UNITED STATES PATENTS 1,982,711 Vickers Dec. 4, 1934 2,214,817 Harrington Sept. 17, 1940 2,643,516 Carlson Jan. 30, 1953 2,656,152 Moon Oct. 20, 1953 2,669,842 Slomer Feb. 23, 1954 53 Towler et al May 15, 1956 2,769,394 Lauck NOV. 6, 1956 2,873,762 Tennis Feb. 17, 1959 

1. IN A HYDRAULIC POWER TRANSMISSION HAVING A PAIR OF DRIVEN PUMPS FOR ACTUATING A PLURALITY OF HYDRAULIC CYLINDERS, A SELECTOR VALVE COMPRISING A HOUSING AND A PLURALITY OF VALVE SPOOLS IN SAID HOUSING SELECTIVELY OPERABLE TO DIRECT FLUID FLOW TO SAID CYLINDERS, PORTS OPERATIVELY ASSOCIATED WITH SAID SPOOLS AND PASSAGES CONNECTED WITH SAID PORTS FORMING AN OPEN CENTER PRESSURE DISTRIBUTION SYSTEM, MEANS CONNECTING ONE OF SAID PUMPS TO ONE END OF SAID OPEN CENTER SYSTEM, MEANS CONNECTING THE OTHER PUMP TO SAID SYSTEM BETWEEN CERTAIN OF SAID SPOOLS, AN UNLOADING VALVE DISPOSED IN SAID HOUSING BETWEEN CERTAIN OF THE VALVE SPOOLS AND OPERABLE TO VENT A PORTION OF THE SYSTEM AT PRE-SELECTED PRESSURE, AND A CHECK VALVE DISPOSED BETWEEN THE UNLOADING VALVE AND THE REMAINDER OF THE SYSTEM AND OPERABLE TO CLOSE TO PREVENT VENTING OF SAID REMAINDER OF THE SYSTEM BY OPERATION OF THE UNLOADING VALVE. 